Reproduction Flashcards
(33 cards)
Pros of asexual reproduction
Faster as no mating or production of gametes
Rapid increase in population size
Individual is able to produce offspring independently
Offspring are genetically identical to the parent
Can quickly colonise a new habitat
Energy and resources can be used for growth and survival
Direct transmission of favourable traits and no dilution because of genetic recombination
Cons of asexual reproduction
Lack of genetic diversity which results in lack of resilience to predators/pathogens
Mutations can be passed onto all offspring resulting in an accumulation of harmful mutations
Limited ability to adapt to environmental changes
Limited evolutionary changes as there’s no natural selection or recombination
Inbreeding depression results in reduced fitness and reproductive stress
Survival success depends on specific environmental conditions and resources
What does sexual reproduction involve?
Gamete production (oogenesis and spermatogenesis)
Male and female reproductive organs
Genetic variation
Hormone control
Establishment and maintenance of pregnancy
Gamete production in females
Oogonia (immature female germ cell)
Oogonia expand by mitosis
Oogonia to oocytes (a developing egg) by meiosis
Produce oocytes
Oocytes leave the ovary (ovulation) and are received by the Fimbriae of the fallopian tubes
If a coitus has taken place, sperm travels to the fallopian tubes resulting in the fertilisation of the oocyte to zygote
Zygote travels to the uterus and implants into the endometrium of the uterus
Mitosis definition
Produces chromosomally genetically identical diploid cells from parental diploid cells
Meiosis definition
Produces gametes with a haploid number of chromosomes from diploid cells
Genetic diversity is attained by the random orientation of bivalents through independent segregation and assortment and recombination of non-sister chromatids
What is a kinetochore
A large protein complex that forms from the centromere
Plays a crucial role in attaching microtubules to the chromosome for proper segregation during cell division
Hormones in the female reproductive cycles
Secreted from the anterior pituitary gland and hypothalamus in the brain
Hypothalamus releases gonadotrophin-releasing hormone (GnRH)
The release is stimulated by factors including bodyweight and stress
Anterior pituitary releases follicle stimulating hormone (FSH) and luteinising hormone (LH)
An increase in oestrogen levels in the follicular phase leads to high levels of LH and induces ovulation
The corpus luteum is stimulated by LH to secrete progesterone and oestrogen, it stays active for 14 days after ovulation
Gamete production in males
Seminiferous tubules are the place of sperm production
Sertoli cells within the seminiferous tubules support and surround developing sperm
Leydig cells produce testosterone in response to LH and generate sperm
FSH (follicle stimulating hormone) maintains Sertoli cells and their response to testosterone
Fertilisation and pregnancy
Growing placenta after implantation generates increasing levels of oestrogen and progesterone
Suppression of the HPO axis (hypothalamic-pituitary-ovarian axis)
Problems faced during fertilisation/pregnancy
Gametes with anomalous number of chromosomes
Genetic defects - trisomy and monosomy
Pregnancy loss
Preeclampsia (high blood pressure) in mother during pregnancy
Also proteinuria which is dangerous for mother and foetus as it can lead to convulsions or stroke in the mother and reduced blood supply to foetus
Ectopic pregnancy
Overview of the placenta
Chorionic villi is where nutrient exchange and waste exchange takes place
Enriched blood arrives via the umbilical vein
Gas exchange as lungs aren’t yet functional
When the baby is born, shunts close and blood circulates as normal
3 stages of labour
Cervix dilates. This is induced by smooth muscle contractions stimulated by oxytocin
Contractions progressively shorten the uterus and push the baby towards the cervix
During cardinal stages the head and shoulders rotate to reduce the diameter that needs to pass in the birth canal
Further uterine contractions separate the placenta and deliver it
Blood vessels compress to reduce bleeding
Stimulation of lactation
Stimulation of nipple leads to sensory neurones that connect with the hypothalamus
Posterior pituitary gland releases oxytocin and the anterior pituitary releases prolactin
Oxytocin stimulates milk release and additional production
Microlecithal egg
Very little or no yolk
In all eutherian mammals (mammals with a placenta)
Some marine animals (tunicates and sea urchins)
Egg/germ cell is surrounded by follicle cells
Centrolecithal egg
Yolk and haploid germ cell located centrally
In insects, other arthropods and cnidaria
Sperm cell can only enter at micropyle as chorion, serosa and vitelline membranes provide mechanical protection
Gas exchange via pores called aeropyles
Mesolecithial eggs
Moderate amount of yolk, unevenly distributed
In amphibians and teleost fish
Yolk is heavy and collects at vegetal pole, the lower half
Macrolecital
Large amount of yolk, unevenly distributed
In birds, reptiles and some mammals (monotremes and platypus)
Egg supports embryo development until the yolk is completely consumed
Copulation meaning
Gamete-containing eggs are fertilised internally by sperm
Viviparous meaning
Delivery of young to an external environment
Eutherian mammals allow the birth of free-living young that have developed inside the mother, after birth still dependent on mother because of lactation
Oviparous
Young leave cleidoic eggs
Marsupials
Key feature is the pouch where the young grow after delivery
Development in the uterus is short and the embryo sits within a shell-type egg
Underdeveloped when born
Pouch provides protection and access to milk
Monotremes
Egg-laying with no internal connection to mother
Long parental care of young
Newborns take up milk via mammary glands that are openings in the skin
Amniotes
Vertebrates with amnion
Reptiles, birds and mammals
Amnion is a membrane surrounding the embryo
